Have labor unions generally raised the wages of unionized workers?
A 2004 paper in the Journal of Labor Research summarizing the results of 100+ studies on union wage effects from 1967 into the 2000s found that unions increased the average wages of unionized workers by about 16%. This is because federal law gives unions an effective monopoly over the labor supply of unionized worksites. However, these increased wages reduced the competitiveness of unionized firms, while driving up taxes and consumer prices. This has led to large-scale losses of union jobs and higher costs of living in states that don't have right-to-work laws.